This application claims the benefit under 35 U.S.C. §119(e) of prior U.S. Provisional Patent Application No. 61/606,282, filed Mar. 2, 2012, which is incorporated in its entirety by reference herein.
The present invention relates to modified carbon blacks, compositions containing the modified carbon blacks, such as elastomeric or rubber compositions, methods of making the modified carbon blacks, as well as methods of using the modified carbon blacks.
Industrially manufactured carbon black is produced by pyrolysis of hydrocarbons at high temperatures under controlled process conditions. Under these conditions, trace levels of polyaromatic hydrocarbons, also known as PAHs, form on the carbon black surface.
Some PAHs have the potential to cause adverse health effects. Although the PAHs that are adhered to the carbon black are not readily available for human exposure, actions are being taken by both EU regulators and customers to reduce the concentration of PAHs in carbon black (See Borm P J, et. al., Formation of PAH-DNA adducts after in vivo and vitro exposure of rats and lung cells to different commercial carbon blacks, Toxicology and Applied Pharmacology, 2005 Jun. 1; 205(2): 157-167). Recent examples include:                Promulgation of EU directive 2007/19/EC which harmonizes the rules for the plastic materials and articles intended to come in contact with food. The directive establishes a Benzo(a)pyrene content of 0.25 mg/kg in carbon black. Previous to this directive, no PAH limit existed for carbon black.        Promulgation of EU directive 2005/69/EC which regulates the content of PAHs in extenders oils used for the production of tires. This directive does not directly regulate the content of PAHs in carbon black; however, the EU has chosen to restrict the content of PAHs in extender oils and blends used to produce tires, in order to reduce the total annual emissions of PAHs, as required in the 1998 Protocol to the 1979 Convention on Long Range Transboundary Air Pollution on Persistent Organic Pollutants.        
The above listed examples demonstrate the growing trend towards lower PAH carbon blacks.
Previous processes have made carbon black with lower PAHs. For instance, U.S. Pat. No. 8,034,316 describes low PAH concentrations in carbon blacks. As described in the patent, the carbon black can be separated from a gas phase in a carbon black manufacturing process at a temperature of from 260° C. to about 950° C., such that the PAH in gas form can be removed, and this temperature is low enough that it does not anneal or degrade the surface of the carbon black and degrade reinforcement performance of the low PAH carbon black. In another description in this patent, the carbon black can be formed during the manufacturing of carbon black, wherein the method includes removing hot tail gas that contains PAH generally at temperatures of from 260° C. to about 950° C. Other methods are further described in this patent, wherein the objective of the patent is not to anneal the surface of the carbon black or otherwise affect surface activity and capacity for reinforcement of elastomeric composites. While the processes described in this patent are effective in forming carbon blacks having low PAHs, the processes require changes in fundamental manufacturing steps and, in some cases, equipment and plant configuration used to create the carbon black particles. Thus the methods described in this patent cannot be carried out within existing manufacturing equipment and/or operating conditions for making particles of carbon black on an industrial scale. It is not possible to alternate between these methods and ordinary methods in the same carbon black plant and it would be necessary to dedicate a line to low PAH carbon black processes. As a result, engineering and operational complexities and costs can be excessive.
While there is a growing desire to have lower PAHs for carbon blacks, any reduction in PAH cannot compromise the desirable performance properties of carbon black in rubber and other applications. Thus, it is desirable to reduce PAH concentration in modified carbon blacks without sacrificing the reinforcement properties achievable by the current carbon blacks and utilizing current manufacturing plants.